Exhaust gas heat exchanger

ABSTRACT

An exhaust gas heat exchanger has a tank, laminated exhaust gas tubes where the exhaust gas flows, a cooling water inlet pipe and a cooling water outlet pipe. The cooling water flows into the tank and flows through water passages between adjacent exhaust gas tubes and between an inner wall of the tank and an outermost exhaust gas tube. Ribs are formed on the exhaust gas tubes so as to lead the cooling water after colliding with an inner wall toward an upstream side of the exhaust gas tubes to prevent the cooling water from being stuck. Otherwise, spaces between an inner wall of a casing and the exhaust gas tubes are regulated to keep the flow rate of the cooling water in the casing so that the cooling water is prevented from being boiled locally by slow flow rate of the cooling water.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application is based upon Japanese Patent Applications No.2001-209335, filed on Jul. 10, 2001, No. 2002-7333, filed on Jan. 16,2002, and No. 2002-494, filed on Jan. 7, 2002, the contents of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to an exhaust gas heat exchangerfor performing heat exchange between exhaust gas generated by combustionand cooling water. Specifically, the present invention relates to anexhaust gas heat exchanger for cooling the exhaust gas in an exhaust gasrecirculation system (i.e., EGR system).

[0004] 2. Related Art

[0005] As shown in FIGS. 1A and 1B, as a prototype made by theinventors, an exhaust gas heat exchanger for cooling the exhaust gas inan EGR system (hereinafter, referred to as an EGR gas heat exchanger300) can be equipped with plural laminated exhaust gas tubes 301disposed in a tank 302 having a rectangular sectional pipe shape. Theexhaust gas tubes 301 have a flat sectional shape, and are attached to acore plate 303 which closes the tank 302. A cooling water inlet pipe 304and a cooling water outlet pipe 305 are connected to the tank 302 sothat cooling water flows in the tank 302 to exchange heat with theexhaust gas passing through the exhaust gas tubes 301.

[0006] In this prototype, the inventors have found that the coolingwater might be boiled at a location close to an upstream side of theexhaust gas tubes 301. The boiling of the cooling water may cause lessefficiency about cooling of the exhaust gas flowing through the exhaustgas tubes 301, and/or rapid increase of inner pressure of the tank 302that may degrade durability of the tank 302.

[0007] The inventors performed an experiment to visually observe thestream of the cooling water flowing in an EGR gas heat exchanger thathas four exhaust gas tubes.

[0008] According to this experiment, when the cooling water inlet pipeis connected to the tank 302 so as to be disposed substantiallyperpendicular to a longitudinal direction of the exhaust gas tubes 301,the cooling water flows into each passage formed between each adjacentexhaust gas tubes 301 so as to turn approximately perpendicular as shownby arrows A (cooling water stream A) in FIG. 2, and it flows toward thecooling water outlet pipe 305. Moreover, some of the cooling watercollides (impacts) with an inner wall 302 a of the tank 302 that isopposite to the cooling water inlet pipe 304 as shown by arrows B(cooling water stream B) in FIG. 2, and then, it flows toward an exhaustgas pipe 301 located at an outermost side.

[0009] However, the cooling water stream A coming from the cooling waterinlet pipe 304 and the cooling water stream B coming through thepassages formed between each adjacent exhaust gas tubes 301 interferewith each other at the gaps formed between the inner walls 302 a and theoutermost exhaust gas pipes 301. As a result, the cooling water iseasily stuck in the vicinity of the root portions of the exhaust gaspipes 301 where the exhaust gas pipes 301 are fixed to the core plate303, as shown in FIGS. 1 and 3.

[0010] This means it may be possible to boil the cooling water when thecooling water is stuck in the vicinity of root portions of the exhaustgas pipes 301 of an upstream side of the exhaust gas. As a result, theefficiency for exchanging heat may be lowered.

[0011] Moreover, the local boiling of water may be caused by low flowingrate of the cooling water in the tank 302.

SUMMARY OF THE INVENTION

[0012] An object of the present invention is to provide an exhaust gasheat exchanger capable of eliminating the boiling of cooling water thatmay be caused by the sticking of the cooling water or caused by lowflowing rate of the cooling water.

[0013] The exhaust gas heat exchanger has a tank, a plurality of exhaustgas passages provided in the tank through which exhaust gas flows and awater passage of the tank through which cooling water flows from acooling water inlet tube to a cooling water outlet pipe.

[0014] According to an aspect of the present invention, a guide isprovided in the tank to lead the cooling water that collides with aninner wall of the tank and flows so as to oppose the cooling watercoming from the cooling water inlet pipe at an upstream side of theexhaust gas passages.

[0015] With this guide, the cooling water that collides the inner wallof the tank is led to a portion where the cooling water can contactupstream side portions of the exhaust gas passages. As a result, thecooling water is prevented from being stuck in the vicinity of theupstream side portions of the exhaust gas passages where the temperatureof the exhaust gas is high, thereby preventing the cooling water frombeing boiled.

[0016] Preferably, the guide is provided in an exhaust gas heatexchanger in which the cooling water inlet pipe is provided on the tankso that the cooling water flows into the tank through the cooling waterinlet pipe in a direction substantially perpendicular to a laminateddirection of the exhaust gas passages and substantially perpendicular toa longitudinal direction of the exhaust gas passages, since the stickingof water easily occurs in this type of an exhaust gas heat exchanger.

[0017] Preferably, the guide is formed so as to protrude from an outerwall of at least one of the exhaust gas passages.

[0018] With this feature, the guide is used as a reinforcing portion forthe passage for the cooling water.

[0019] According to another aspect of the present invention, a firstbonnet for introducing the exhaust gas to the plurality of exhaust gastubes is provided at one side of the tank, and a second bonnet forgathering the exhaust gas passing through the exhaust gas tubes.Moreover, a first plate is provided between the first bonnet and acooling water passage for isolating the cooling water from the firstbonnet, and a second plate is provided between the second bonnet and thecooling water passage for isolating the cooling water from the secondbonnet. Furthermore, a guide is provided in the tank to lead the waterthat collides at an inner wall of the tank and flows so as to oppose thewater coming from the cooling water inlet pipe to the vicinity of theroot portions of the plurality of exhaust gas tubes that are attached tothe first plate.

[0020] With this guide, the water that collides at an inner wall of thetank is led to the root portions of the plurality of exhaust gas tubeswhere the plurality of exhaust gas tubes are attached to the firstplate. As a result, the cooling water is prevented from sticking in thevicinity of the root portions of the plurality of exhaust gas tubeswhere the exhaust gas having high temperature flows into the pluralityof exhaust gas tubes, thereby preventing the cooling water from beingboiled.

[0021] According to further aspect of the present invention, a partitionwall is provided between an outermost water passage for the coolingwater that is formed between an inner wall of the tank and an outermostexhaust gas passage and an inner water passage for the cooling waterthat is formed between adjacent exhaust gas passages.

[0022] With this partition wall, after the cooling water collides withthe inner wall of the tank, the cooling water is prevented from flowinginto the outermost passage formed between the inner wall and theoutermost exhaust gas passage. Therefore, sticking of the cooling waterat an upstream side of the plurality of exhaust gas passages, which iscaused by the flow of the cooling water toward the outermost waterpassage formed between the inner wall and the outermost exhaust gaspassage, is prevented, thereby preventing the cooling water from beingboiled.

[0023] According to further another aspect of the present invention, anexhaust gas heat exchanger has a casing, a plurality of exhaust gastubes provided in the casing through which exhaust gas flows and each ofwhich has flat sectional shape, and a fluid passage of the casingthrough which fluid flows from a fluid inlet to a fluid outlet. In thisexhaust gas heat exchanger, adjacent exhaust gas tubes are spaced apartfrom each other at a distance of δt. Moreover, an outermost exhaust gastube of the plurality of exhaust gas tubes is spaced apart from an innerwall of the casing that faces the outermost exhaust gas tube at adistance of δin1 in a direction generally perpendicular to an inflowdirection of the fluid coming into the casing through the fluid inletand generally perpendicular to a longitudinal direction of the pluralityof exhaust gas tubes. The distance of δin1 is substantially equal to thedistance of δt to prevent flow rate of the fluid from being loweredlower than a predetermined rate.

[0024] According to further another aspect of the present invention, anexhaust gas heat exchanger has a casing, a plurality of exhaust gastubes provided in the casing through which exhaust gas flows and each ofwhich has flat sectional shape, and a fluid passage provided in thecasing through which fluid flows from a fluid inlet to a fluid outlet.In this exhaust gas heat exchanger, the fluid inlet is provided on thecasing so that the fluid can flow into the casing in a directionsubstantially perpendicular to a longitudinal direction of the pluralityof exhaust gas tubes. Moreover, an outermost exhaust gas tube of theplurality of exhaust gas tubes is arranged in the casing so as to bespaced apart from an inner wall of the casing at a distance of δin1 in adirection generally perpendicular to an inflow direction of the fluidfrom the fluid inlet and in a direction generally perpendicular to thelongitudinal direction of the plurality of exhaust gas tubes. Thedistance δin1 is equal to or greater than 1 mm but less than or equal to5 mm.

[0025] With this distance δin1, a flow rate of the fluid flowing througha space between the outermost exhaust gas tube and the inner wall of thecasing can be prevented from being lowered lower than a predeterminedflow rate.

[0026] According to further another aspect of the present invention, anexhaust gas heat exchanger has a casing, a plurality of exhaust gastubes provided in the casing through which exhaust gas flows and each ofwhich has flat sectional shape, and a fluid passage of the casingthrough which fluid flows from a fluid inlet to a fluid outlet. In thisexhaust gas heat exchanger, the fluid outlet is provided on the casingso that the fluid flowing through the casing flows out from the casingin a direction generally perpendicular to a longitudinal direction ofthe plurality of exhaust gas tubes and in a direction generally parallelwith an arranged direction of the plurality of exhaust gas tubes. Anadjacent exhaust gas tubes are spaced apart from each other at adistance of δt. Moreover, an outermost exhaust gas tube of the pluralityof exhaust gas tubes is spaced apart from an inner wall of the casingthat faces the outermost exhaust gas tube at a distance of δout in thevicinity of the fluid outlet with respect to the fluid inlet in adirection generally perpendicular to the longitudinal direction of theplurality of exhaust gas tubes and generally parallel with the arrangeddirection of the plurality of exhaust gas tubes. The distance δout isgreater than the distance of δt.

[0027] With this feature, pressure loss of the fluid in the casing isprevented from increasing, thereby preventing mass flow of the fluidfrom decreasing. Therefore, the effect of heat exchange between thefluid and the exhaust gas is prevented from decreasing, and localboiling of the fluid is prevented.

[0028] Preferably, the distance δout is greater than or equal to 5 mm.

[0029] Incidentally, the plurality of exhaust gas tubes may be spacedapart from an inner wall of the casing at a distance of δin2 in adirection generally parallel with the inflow direction of the fluidcoming into the casing through the fluid inlet and generallyperpendicular to a longitudinal direction of the plurality of exhaustgas tubes. The distance δin2 is greater than or equal to the distanceδout. This distance δin2 improves the distribution efficiency of thefluid to each space between the adjacent exhaust gas tubes and allowsthe pressure loss in the vicinity of the fluid inlet to be reduced.

[0030] Preferably, the distance δin2 is greater than or equal to 1 mm tosecure the distribution efficiency of the fluid to each space betweenthe adjacent exhaust gas tubes and the reduction of the pressure loss.

[0031] Other features and advantages of the present invention willbecome more apparent from the following detailed description made withreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0032]FIG. 1A is a partial cross sectional view showing an EGR gas heatexchanger in the related art;

[0033]FIG. 1B is a partial cross sectional view of the EGR gas heatexchanger in the related art taken along line IB-IB in FIG. 1A;

[0034]FIG. 2 is a partial cross sectional view similar to FIG. 1B of theEGR gas heat exchanger in the related art;

[0035]FIG. 3 is a partial cross sectional view of the EGR gas heatexchanger taken along line III-III in FIG. 1A;

[0036]FIG. 4 is a schematic view of an EGR system according to thepresent invention;

[0037]FIG. 5A is a partial cross sectional view of an EGR gas heatexchanger in a first embodiment of the present invention;

[0038]FIG. 5B is a partial cross sectional view of the EGR gas heatexchanger in the first embodiment of the present invention taken alongline VB-VB in FIG. 5A;

[0039]FIG. 6A is a partial cross sectional view of an EGR gas heatexchanger in a second embodiment of the present invention;

[0040]FIG. 6B is a partial cross sectional view of the EGR gas heatexchanger in the first embodiment of the present invention taken alongline VIB-VIB in FIG. 6A;

[0041]FIG. 7 is a cross sectional view of the EGR gas heat exchanger inthe first embodiment of the present invention taken along line VII-VIIin FIG. 6B;

[0042]FIG. 8 is a perspective view of the EGR cooler in third and fourthembodiments of the present invention;

[0043]FIG. 9A is a partial cross sectional view of an EGR cooler in thethird embodiment of the present invention;

[0044]FIG. 9B is a partial cross sectional view of the EGR cooler in thethird embodiment of the present invention taken along line IXB-IXB inFIG. 9A;

[0045]FIG. 10 is a cross sectional view of the EGR cooler in the thirdembodiment of the present invention taken along line X-X in FIG. 9B;

[0046]FIG. 11 is a cross sectional view of the EGR cooler in the thirdembodiment of the present invention taken along line XI-XI in FIG. 9B;

[0047]FIG. 12 is a cross sectional view of the EGR cooler in the thirdembodiment of the present invention taken along line XII-XII in FIG. 9B;

[0048]FIG. 13 is a cross sectional view of the EGR cooler in the fourthembodiment of the present invention similar to FIG. 11;

[0049]FIG. 14 is a perspective view of the EGR cooler in the otherembodiment of the present invention;

[0050]FIG. 15 is a perspective view of the EGR cooler in the otherembodiment of the present invention; and

[0051]FIG. 16 is a partial cross sectional view of an EGR cooler in theother embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0052] Specific embodiments of the present invention will now bedescribed hereinafter with reference to the accompanying drawings inwhich the same or similar component parts are designated by the same orsimilar reference numerals.

[0053] (First Embodiment)

[0054] A first preferred embodiment of the present invention will be nowdescribed with reference to FIGS. 4, 5A and 5B. In the first embodiment,the present invention is typically applied to an EGR cooler of anexhaust gas recirculation system (EGR system) for a diesel engine 200(internal combustion system). FIG. 1 shows an exhaust gas heat exchanger100 (hereinafter, referred to as an EGR gas heat exchanger) that relatesto the first embodiment and a second embodiment described later.

[0055] The EGR system includes an exhaust gas recirculation pipe 210through which a part of the exhaust gas discharged from the engine 200returns to an intake side of the engine 200. An EGR valve 220 foradjusting the amount of exhaust gas recirculation in accordance with anoperational state of the engine 200 is disposed in the exhaust gasrecirculation pipe 210. The EGR gas heat exchanger (EGR cooler) 100 isdisposed between an exhaust gas side of the engine 200 and the EGR valve220 so that heat exchange is performed between the exhaust gasdischarged from the engine 200 and cooling water(i.e., engine-coolingwater).

[0056] Next, a structure of the EGR gas heat exchanger 100 will bedescribed with reference to FIGS. 5A and 5B.

[0057] EGR gas heat exchanger 100 comprises plural, in this case, fourexhaust gas tubes 101 each of which has a flat rectangular crosssection, and each of which is formed by joining two plates (not shown)facing each other. As shown in FIG. 7, an inner fin 101 b, which is forpartitioning the space formed in each exhaust gas tube 101 to formplural fine passages by being folded many times, is disposed in eachexhaust gas tube 101. A tank 102 has a tubular shape and a flatrectangular cross section. This tank and the exhaust gas tubes 101 forma heat exchanging core. The exhaust gas tubes 101 are laminated in thetank 102 so as to be disposed in substantially parallel with each other.Moreover, a longitudinal direction of the exhaust gas tubes 101 and alongitudinal direction of the tank 102 match with each other in the tank102.

[0058] The tank 102 is closed at both of its side ends by core plates103 so that respective side ends of each exhaust gas tube 101 in thetank 102 penetrate the respective core plates 103 and are supported bythe respective core plates 103.

[0059] A cooling water inlet pipe 104 is connected to the tank 102 atthe vicinity of root portions 101 a at upstream side portions of theexhaust gas tubes 101. Moreover, the cooling water inlet pipe 104 isconnected to the tank so as to be disposed substantially perpendicularto a laminated direction of the exhaust gas tubes 101 so that thecooling water can easily enter each gap formed between each adjacentlaminated exhaust gas tubes 101 when the cooling water flows into thetank 102 through the cooling water inlet pipe 104. A cooling wateroutlet pipe 105 is connected to the tank 102 at the vicinity ofdownstream side portions of the exhaust gas tubes 101 so that the tank102 serves as a passage for the cooling water. The main stream of thecooling water substantially follows the stream of the exhaust gaspassing through the exhaust gas tubes 101 in the tank 102.

[0060] Bonnets 106, 107 are connected to the both side ends of the tank102 so that edges of both core plates 103 are folded in oppositedirections with regard to the bonnets 106, 107 as shown the figures, andare overlapped by end portions of the bonnets 106, 107. An exhaust gasinlet 106 a is formed in the bonnet 106 disposed at a cooling waterinlet pipe side that is for introducing the exhaust gas to the bonnet106. An exhaust gas outlet 107 a is formed in the bonnet 107 disposed ata cooling water outlet pipe side that is for exhausting the exhaust gasfrom the bonnet 106 to the outside. Both of the bonnets 106, 107 have aquadrangular pyramid-like shape so that the duct cross sectional areaincreases toward the heat exchanging core.

[0061] Hereinafter, main portion of the present invention will bedescribed. A pair of ribs 108 a, 108 b are formed as guides on both mainsurfaces of each exhaust gas pipe 101 at portions of both main surfacesclose to the exhaust gas inlet 106 a by an embossing process. As shownin FIG. 5A, the ribs 108 a, 108 b have an elliptic shape so that anellipse extends from an end portion of the exhaust gas tube 101 in thewidth direction (longitudinal direction of the cross section) to thevicinity of a central portion of the passage for the cooling water inthe width direction so as to be disposed in a cross direction withrespect to the longitudinal direction of the exhaust gas tubes 101 andthe longitudinal direction of the tank 102 that matches a direction ofthe main stream of the cooling water. A small passage through which thecooling water can pass is formed between the pair of ribs 108 a, 108 b.Both ribs 108 a, 108 b formed on the exhaust gas tube 101 contact to theother ribs 108 a, 108 b formed on adjoining one of the exhaust gas tubes101. The respective pairs of ribs 108 a, 108 b formed on the respectiveouter main surfaces of the respective outermost exhaust gas tubes 101 omcontact to a respective protrusion 109 formed on the inner wall of thetank in the laminated direction of the exhaust gas tubes 101. Theprotrusions 109 have a shape similar to that of the pair of ribs 108 a,108 b.

[0062] In this EGR gas heat exchanger 100 described above, the exhaustgas introduced from the exhaust gas inlet 106 a passes through thebonnet 106 and each of the exhaust gas tubes 101. Then, the exhaust gascooled down by the cooling water flowing around each of the exhaust gastubes 101 is exhausted from the exhaust gas outlet 107 a through thebonnet 107.

[0063] The cooling water flows into the tank 102 through the coolingwater inlet pipe 104 and passes through gaps formed between eachadjacent exhaust gas tubes 101 and gaps formed between the inner wall ofthe tank 102 and each of the outermost exhaust gas tubes 101 om. At thetime when the cooling water flows into the tank 102 through the coolingwater inlet pipe 104, the cooling water coming into the tank 102 along adirection substantially perpendicular to the longitudinal direction ofthe tank 102. Therefore, the cooling water after coming into the tank102 through the cooling water inlet pipe 104 collides with an inner wall102 a of the tank 102 that is opposite to the cooling water inlet pipe104. Then, the cooling water flows so as to be divided toward therespective outermost exhaust gas tubes 101 om in the laminated directionof the exhaust gas tubes 101 (up-down direction in FIG. 5B). The dividedstreams of the cooling water go to, for example, the gaps formed betweenthe inner wall of the tank 102 and each of the outermost exhaust gastubes 101 om, and pass the gaps along the respective ribs 108 b formedon the respective outermost exhaust gas tubes 101 om to forcibly go tothe vicinity of the respective root portions 101 a (end portions ofupstream side) of the respective outermost exhaust gas tubes 101 om asshown by arrow C in FIG. 5A.

[0064] The stream C of the cooling water along the rib 108 b is mergedwith the stream A of the cooling water coming into the tank from thecooling water inlet pipe 104 between the ribs 108 a and 108 b, and then,goes toward the cooling water outlet pipe 105.

[0065] According to the first embodiment, the stream C can flow alongthe rib 108 b so as to pass the upstream side of the outermost exhaustgas tubes 101 om. Therefore, the cooling water is prevented from beingstuck at the upstream side of the exhaust gas, thereby preventing thecooling water from being boiled partially.

[0066] In this embodiment, the ribs 108 b are formed on each exhaust gastube 101. Therefore, the stream C flowing along the rib 108 b can occurat any gap formed between adjacent exhaust gas tubes 101 as well as thegaps formed between the inner wall of the tank 102 and the outermostexhaust gas tubes 101 om.

[0067] In this embodiment, the respective ribs 108 a, 108 b contact tothe other respective ribs 108 a, 108 b formed on adjacent exhaust gastube 101. Also, the respective pairs of ribs 108 a, 108 b formed on therespective outer main surfaces of the respective outermost exhaust gastubes 101 om contact to the respective protrusions 109 formed on theinner wall of the tank 102. Therefore, the ribs 108 a, 108 b and theprotrusions 109 serve as reinforcement parts for reinforcing the exhaustgas tubes 101 as well as the tank and the passage for the cooling water.

[0068] In the producing process of the EGR gas heat exchanger 100, whenthe exhaust gas tubes 101 are connected with each other and solderedwith each other using solder, the proper load can be supplied to theexhaust gas tubes 101 and the inner fin 101 b in each exhaust gas tube101 due to the existence of the ribs 108 a, 108 b, whereby failure ofsoldering can be prevented. Also, the ribs 108 a, 108 b keep intervalsconstant between every two of the exhaust gas tubes 101 and formedbetween the inner wall of the tank 102 and the outermost exhaust gastubes 101 om.

[0069] Although the ribs 108 a, 108 b in this embodiment are formedusing an embossing process, they can be formed using the other ways. Forexample, the ribs 108 a, 108 b can be formed discretely from the exhaustgas tubes 101. Also, the shape of the ribs 108 a, 108 b is not limitedto the elliptic shape. The shape of the rib may be varied as long as itflows the cooling water after colliding the inner wall of the tanktoward the upstream side of the exhaust gas tubes 101 so as to regulatethe stream of the cooling water as shown in the FIG. 5A. Moreover, theribs can be formed only on the outermost exhaust gas tubes 101 om sincethe cooling water after colliding the inner wall 102 a of the tank 102especially easily flows toward the gaps formed between the inner wall ofthe tank 102 and the outermost exhaust gas tubes 101 om. Also, thenumber of the exhaust gas tubes 101 in the tank 102 is not limited tofour.

[0070] (Second Embodiment)

[0071] In the above embodiment, the ribs are used for leading thecooling water after colliding with the inner wall 102 a of the tank 102toward the upstream side of the exhaust gas tubes 101.

[0072] In this embodiment, instead of the ribs, partition walls(anti-reflection boards) are used to prevent the cooling water fromflowing into the gaps formed between the inner wall of the tank 102 andthe outermost exhaust gas tubes 101 om.

[0073] As shown in FIGS. 6A, 6B, and 7, the exhaust gas tubes 101 arelaminated in 4 layers as shown in the first embodiment. Moreover, theyare divided into two parts in each layer thereof. Inner fins 101 b andlouvers 101 c are formed in each exhaust gas tube 101. The louvers 101 cfixed to the inner fines 101 b are for causing vortex flow in the finepassages.

[0074] The partition walls 110(110 a) are formed between the inner wall102 a of the tank 102 and the exhaust gas tubes 101. The partition walls110 a are formed by folding a plate to form the partition. That plate isdisposed between the gap formed between the inner wall 102 a of the tank102 and the exhaust gas tubes 101 so that folded portions of the platecontact to the inner wall 102 a of the tank and the exhaust gas tubes101. As shown in FIG. 7, the respective water passages 111 for thecooling water, which are formed between adjacent exhaust gas tubes 101,are partitioned from the respective water passages 112 for the coolingwater, which are formed between the inner wall of the tank 102 and theoutermost exhaust gas tubes 101 om, by the partition walls 110 a.

[0075] The cooling water flowing into the tank 102 through the coolingwater inlet pipe 104 flows into each water passage 111, 112 as shown byarrows E in FIGS. 6A and 7. The cooling water flowing into the waterpassages 111 is prevented from flowing into the water passages 112, andflows toward the cooling water outlet pipe 105. Similar to the firstembodiment, the occurrence of the stuck water at the upstream side ofthe exhaust gas tubes 101, which may be caused by the interfering of thecooling water after colliding with the inner wall 102 a against thecooling water just flowing into the tank 102 through the cooling waterinlet tube 104, is prevented. Therefore, the cooling water can beprevented from being boiled partially.

[0076] Although the partition walls are formed as the anti-reflectionplate by folding the plate in this embodiment, they can be formed by theother ways. Also, the shape or size of the walls is not limited to thatof this embodiment. Moreover, the partition walls may be used forsubstantially preventing the cooling water in the water passages 111after impacting the inner wall 102 a of the tank 102 from flowing intothe water passages 112. Therefore, a small gap can be allowed betweenthe partition walls and the exhaust gas tubes 101 or between thepartition walls and the inner wall 102 a of the tank 102 as long as thecooling water is substantially prevented from flowing into the waterpassages 112 even if the small gap exists.

[0077] In the above embodiments, the size, shape, a portion to beformed, or the number of ribs or partition walls may be varied to effectthe regulation of the stream of the cooling water.

[0078] (Third Embodiment)

[0079] In the above-described embodiments, the flow regulation of thecooling water has been discussed. In embodiments described later, theflow rate of fluid for cooling the exhaust gas flowing through theexhaust gas tubes, i.e., in this embodiment, the flow rate of coolingwater will be discussed to prevent the cooling water from boilinglocally.

[0080] An EGR cooler (i.e., an EGR gas heat exchanger) is perspectivelyshown in FIG. 8. EGR gas, i.e., exhaust gas from the engine 200 as shownin FIG. 4 flows into the EGR cooler at a right side in the figure, flowsthrough the EGR cooler, and then, flows out from the EGR cooler at aleft side in the figure. Cooling water flows into the EGR cooler througha cooling water inlet pipe (a fluid inlet) 204 to exchange heat with theexhaust gas flowing through the EGR cooler. The cooling water flows outfrom the EGR cooler through a cooling water outlet pipe 205 (a fluidoutlet).

[0081] In FIG. 8, XI-XI and XII-XII mean cross sectional view pointsthat are shown in FIGS. 11 and 12, respectively.

[0082]FIGS. 9A and 9B and numerals thereon are figures and numeralssimilar to FIGS. 5A and 5B, and therefore, the explanation thereof willbe omitted.

[0083] In FIGS. 9A and 9B, a distribution joint 206 is for distributingthe exhaust gas to the exhaust gas tubes 201. A gathering joint 207 isfor gathering the exhaust gas passing through the exhaust gas tubes 201.Joint portions 206 a and 207 a of the joints 206 and 207 are connectedto exhaust gas recirculation pipe 210 shown in FIG. 4.

[0084] As shown in FIG. 10, each exhaust gas tube 201 has a flatsectional shape through which the exhaust gas flows. The plural exhaustgas tubes are laminated in a shortest length direction, i.e., athickness direction of the exhaust gas tube 201 (an up-and-downdirection in FIG. 10), with a space 201 a interposed between adjacentexhaust gas tubes 201. The exhaust gas tubes 201 are arranged in tworows in a width direction of the exhaust gas tube 201 (a lateraldirection in FIG. 10). In each row, four exhaust gas tubes 201 arelaminated. Each exhaust gas tube has two plates 201 b, 201 c that arepressed into “C” character-like sectional shape and soldered usingcopper solder or the like with each other to form the shape thereof ,and has a folded fin 201 c to improve the heat exchange efficiencybetween the exhaust gas and cooling water by increasing contacting area(heat conducting area) between the exhaust gas and the fin 201 c. Thefolded fin is connected to the plates 201 b and 201 c by solder usingcopper solder or the like.

[0085] The space 201 a is kept by contacting tops of protrusions 201 ethat are protruded from the plates 201 b and 201 c by a press process orthe like. The protrusions 201 e are discretely formed on the exhaust gastubes 201 so as not to be formed on portions in the vicinity of thecooling water inlet pipe 204 and cooling water outlet pipe 205.

[0086] For example, the exhaust gas tubes 201 and folded fins 201 d aremade from stainless steal that is excellent in corrosion resistance andheat resistance.

[0087] The casing 202 is a rectangular pipe in which the exhaust gastubes 201 is arranged and through which the cooling water flows aroundthe exhaust gas tubes 201. The casing 202 also is made of metal that isexcellent in corrosion resistance and heat resistance, for example,stainless steal plates 202 b and 202 c fixed with each other bysoldering using copper solder or the like.

[0088] The cooling water inlet pipe 204 is provided on the casing 202 sothat the cooling water flows into the casing 202 in a directionsubstantially perpendicular to a longitudinal direction of the exhaustgas tubes 201 and substantially parallel with flat main surfaces of theexhaust gas tubes 201. On the other hand, the cooling water outlet pipe205 is provided on the casing 202 so that the cooling water flows outfrom the casing 202 in a direction substantially perpendicular to thelongitudinal direction of the exhaust gas tubes 201 and substantiallyperpendicular to the flat main surfaces of the exhaust gas tubes 201.

[0089] The cooling water inlet pipe 204 and cooling water outlet pipe205 are for being connected to external cooling water pipes.

[0090] As shown in FIG. 11, spaces 202 g extend between an inner wall ofthe casing 202 and outermost exhaust gas tubes 201 om in a directiongenerally parallel with the inflow direction of the cooling waterflowing into the casing through the cooling water inlet pipe 204. Thewidth of the space 202 g in a laminated direction of the exhaust gastubes 201, i.e., in a direction generally perpendicular to the inflowdirection of the cooling water and perpendicular to a longitudinaldirection of the exhaust gas tubes 201 (perpendicular to a sheet of thefigure), is δin1, as shown in FIG. 11. The width δin1 of the spaces 202g is almost equal to the width δt of the space 201 a between adjacentexhaust gas tubes 201.

[0091] Meanwhile, as shown in FIG. 12, spaces 202 h extend between theinner wall of the casing 202 and the outermost exhaust gas tubes 201 omin the vicinity of the cooling water outlet pipe 205 in a directiongenerally perpendicular to an outflow direction of the cooling waterflowing out from the casing 202 through the cooling water outlet pipe205. The width of the spaces 202 h in the laminated direction of theexhaust gas tubes 201, i.e., in a direction generally parallel with theoutflow direction of the cooling water and perpendicular to thelongitudinal direction of the exhaust gas tubes 201 (perpendicular to asheet of the figure), is δout, as shown in FIG. 12 (as understood fromFIGS. 8, 9A and 9B). The width δout of the spaces 202 h is greater thanthat of the space 201 a between adjacent exhaust gas tubes 201.

[0092] Specifically, the width δin1 is equal to 1 mm or more but equalto 5 mm or less (2 mm in this embodiment). The width δout is equal to 5mm or more (5 mm in this embodiment).

[0093] The lower limit of the width δin1 is defiled in such a degreethat the spaces 202 g that serve as cooling water passages are preventedfrom being clogged with extraneous substance in the cooling water.Meanwhile, the upper limit of the width δin1 is defiled in such a degreethat the flow rate of the cooling water flowing through the spaces 202 gis not lowered lower than a predetermined rate.

[0094] Most of the cooling water flowing into the casing 202 through thecooling water inlet pipe 204 flows through the spaces 201 a betweenspaces 201 a facing the cooling water inlet pipe 204, i.e., spaces 201 aformed between two exhaust gas tubes 201 in the second and third layers.Then, most of the cooling water collides with the inner wall of thecasing 200 that is opposite to the cooling water inlet pipe 204 (a rightside wall in FIG. 11).

[0095] Therefore, the mass flow of the cooling water is smaller in thespaces 202 g than in the spaces 202 a because the spaces 202 g arefarther away from the space 201 a between the exhaust gas tubes 201 inthe second and third layers in the direction perpendicular to the inflowdirection of the cooling water and perpendicular to the longitudinaldirection of the exhaust gas tubes 201 (perpendicular to a sheet of thefigure). Accordingly, the flow rate in the spaces 202 g become small. Asa result, the cooling water might be likely boiled at the spaces 202 g.

[0096] In this embodiment, the spaces 202 g are regulated in width ofδin1 similar to that of δin1 of the spaces 201 a to prevent the flowrate therein from being lowered lower than the predetermined rate.Therefore, the local boiling of the cooling water is prevented at thespaces 202 g.

[0097] Similar to the spaces 202 g, the width δt of the spaces 201 a isselected between the width with which the spaces 201 a are preventedfrom being clogged with extraneous substance in the cooling water andthe width with which the flow rate of the cooling water flowing throughthe spaces 201 a is not lowered lower than the predetermined rate.

[0098] To the contrary, the cooling water is collected in the vicinityof the cooling water outlet pipe 205 after flowing through the casing202. Therefore, if the width δout of the spaces 202 h was small, thepressure loss might be increased at the spaces 202 h that might reducethe amount of the cooling water flowing into the EGR cooler 200. In thissituation, the local boiling might be caused.

[0099] In this embodiment, the width δout of the spaces 202 h in thevicinity of the cooling water outlet pipe 205 is greater than the widthδt of the spaces 201 a between adjoining exhaust gas tubes 201 toprevent the pressure loss from being increased. Therefore, the coolingwater flowing into the casing 202 is prevented from decreasing, therebypreventing the local boiling of the cooling water from occurring andpreventing cooling efficiency of the exhaust gas from being lowered.

[0100] Moreover, as shown in FIG. 11, spaces 202 j are formed betweeninner walls of the casing 202 that are disposed generally perpendicularto the inflow direction of the cooling water and sides of the exhaustgas tubes 201. The width of the spaces 202 j in a direction generallyparallel with the inflow direction of the cooling water, i.e., in aparallel direction of the figure, is δin2. The width δin2 issubstantially equal to the width δt of the spaces 201 a betweenadjoining exhaust gas tubes 201 for the same reason described above.

[0101] (Fourth Embodiment)

[0102] In this embodiment, differences between the third embodiment andthis embodiment will be mainly described.

[0103] As shown in FIG. 13, the width δin2 of the spaces 202 j isgreater than the width δt of the spaces 201 a. Specifically, the widthδin2 of the spaces 202 j is equal to 5 mm or more (5 mm in thisembodiment), the width δin1 of the spaces 202 g is equal to 1 mm or morebut equal to 5 mm or less (2 mm in this embodiment), and the width δoutof the spaces 202 h is equal to 5 mm or more (5 mm in this embodiment).

[0104] With this feature, the distribution efficiency of the coolingwater to each space 201 a between each adjacent exhaust gas tube 201 inthe laminated direction can be improved. Moreover, the pressure loss inthe vicinity of the cooling water outlet pipe 205 can be reduced.

[0105] Although the spaces 202 h are greater in width than the spaces202 g in the above-described embodiments, it is not necessarily to formthe wider spaces 202 h. Instead of changing the shape of the casing 202,the size or the location of the exhaust gas tubes 201 can be varied tomatch the size dimension of the width of spaces 202 g with that of thespaces 201 a.

[0106] The space between the exhaust gas tubes 201 and the inner wall ofthe casing 202 is formed wider in the vicinity of the cooling wateroutlet pipe 205 at entirely circumference as shown in FIG. 8. However,as shown in FIG. 14, the wider portion of the casing 202 may be limitedto a portion where the spaces 202 h are located between the inner wallof the casing 202 and the outermost exhaust gas tubes 201 om in thevicinity of the cooling water outlet pipe 205 in the laminated directionof the exhaust gas tubes 201 and a portion close to the outlet side withrespect to the inlet side of the casing where the spaces 202 h arelocated between the inner wall of the casing 202 and the outermostexhaust gas tubes 201 om at an opposite side of the portion where thecooling water outlet pipe 205 is located in the laminated direction.

[0107] Moreover, the spaces 202 h in the outlet side of the casing 202may be formed so that the width thereof is identical to that of thespaces 201 a between adjacent exhaust gas tubes 201 similar to thespaces 202 g in the inlet side of the casing 202.

[0108] Moreover, as shown in FIG. 16, ribs 208 a or ribs 208 b also canbe formed on each exhaust gas tube 201 that are shown FIGS. 5A and 5B soas to regulate the flow of the cooling water in addition to keeping theflow rate of the cooling water in the casing 202 by adjusting the sizeof the spaces.

[0109] While the present invention has been shown and described withreference to the foregoing preferred embodiment, it will be apparent tothose skilled in the art that changes in form and detail may be thereinwithout departing from the scope of the invention as defined in theappended claims.

What is claimed is:
 1. An exhaust gas heat exchanger comprising: aplurality of exhaust gas passages each of which has a flat sectionalshape and through which exhaust gas generated by combustion flows,wherein the plurality of exhaust gas passages are laminated so as to bedisposed in substantially parallel with each other; a tank containingthe plurality of exhaust gas passages; a water passage formed in thetank through which cooling water flows to exchange heat with the exhaustgas passing through the plurality of exhaust gas passages; a coolingwater inlet pipe disposed on the tank, through which the cooling waterflows into the tank; a cooling water outlet pipe disposed on the tank,through which the cooling water is exhausted from the tank; and a guideprovided in the water passage for leading the cooling water collidingwith an inner wall of the tank toward an upstream side of at least oneof the plurality of exhaust gas passages.
 2. An exhaust gas heatexchanger according to claim 1, wherein the cooling water inlet pipe isprovided on the tank so that the cooling water flows into the tank alonga direction substantially perpendicular to a laminated direction of theplurality of exhaust gas passages and substantially perpendicular to alongitudinal direction of the plurality of exhaust gas passages.
 3. Anexhaust gas heat exchanger according to claim 1, wherein the guide isformed on at least one of the plurality of exhaust gas passages so as toprotrude from an outer wall thereof to the water passage.
 4. An exhaustgas heat exchanger according to claim 1, wherein the guide is formed onat least an outermost one of the plurality of exhaust gas passages. 5.An exhaust gas heat exchanger according to claim 1, wherein the guide isformed on all of the plurality of exhaust gas passages to protrudetoward the water passage to regulate streams of the cooling water in thetank.
 6. An exhaust gas heat exchanger according to claim 1, wherein theguide is formed on an inner wall of the tank that opposes an outermostone of the plurality of exhaust gas passages in a laminated direction ofthe plurality of exhaust gas passages.
 7. An exhaust gas heat exchangeraccording to claim 2, wherein the guide has a longitudinal shape andprovided in the water passage so that its longitudinal direction issubstantially perpendicular to a longitudinal direction of the pluralityof exhaust gas passages.
 8. An exhaust gas heat exchanger according toclaim 3, wherein the guide is embossed from the outer wall of at leastone of the plurality of exhaust gas passages.
 9. An exhaust gas heatexchanger comprising: a plurality of exhaust gas tubes each of which hasa flat sectional shape and through which exhaust gas generated by acombustion flows, wherein the plurality of exhaust gas passages arelaminated so as to be disposed in substantially parallel with eachother; a tank containing the plurality of exhaust gas tubes; a waterpassage formed in the tank through which cooling water flows to exchangeheat with the exhaust gas passing through the plurality of exhaust gastubes; an inlet bonnet communicating with upstream end portions of theplurality of exhaust gas tubes to supply the exhaust gas to all of theplurality of exhaust gas tubes; an outlet bonnet communicating withdownstream end portions of the plurality of exhaust gas tubes to gatherthe exhaust gas passing through the plurality of exhaust gas tubes; anupstream side core plate connected to the upstream end portions of theplurality of exhaust gas tubes to isolate the water passage from theexhaust gas; a downstream side core plate connected to the downstreamend portions of the plurality of exhaust gas tubes to isolate the waterpassage from the exhaust gas; a cooling water inlet pipe disposed on thetank through which the cooling water flows into the tank; a coolingwater outlet pipe disposed on the tank through which the cooling wateris exhausted from the tank; and a guide provided in the water passagefor leading the cooling water colliding with an inner wall of the tanktoward a root portion side of at least one of the plurality of exhaustgas passages, which is a vicinity of the upstream side core plate. 10.An exhaust gas heat exchanger according to claim 9, wherein the guide isformed on at least one of the plurality of exhaust gas tubes so as toprotrude from an outer wall thereof to the water passage.
 11. An exhaustgas heat exchanger according to claim 9, wherein the guide is formed onan inner wall of the tank that opposes an outermost one of the pluralityof exhaust gas tubes in a laminated direction of the plurality ofexhaust gas tubes.
 12. An exhaust gas heat exchanger according to claim10, wherein the guide is embossed from the outer wall of at least one ofthe plurality of exhaust gas tubes.
 13. An exhaust gas heat exchangercomprising: a plurality of exhaust gas passages each of which has a flatsectional shape and through which exhaust gas generated by a combustionflows, wherein the plurality of exhaust gas passages are laminated so asto be disposed in substantially parallel with each other; a tankcontaining the plurality of exhaust gas passages; a water passage formedin the tank through which cooling water flows to exchange heat with theexhaust gas passing through the plurality of exhaust gas passages; acooling water inlet pipe disposed on the tank so as to oppose an innerwall of the tank through which the cooling water flows into the tank; acooling water outlet pipe disposed on the tank through which the coolingwater is exhausted from the tank; and a partition wall provided in a gapformed between the inner wall of the tank and the plurality of exhaustgas passages for isolating an inner water passage that is formed betweenadjacent plurality of exhaust gas passages from an outer water passagethat is formed between an outermost one of the plurality of exhaust gaspassages.
 14. An exhaust gas heat exchanger according to claim 13,wherein the partition wall is a folded plated disposed between the gapformed between the inner wall of the tank and the plurality of exhaustgas passages.
 15. An exhaust gas heat exchanger comprising: a pluralityof exhaust gas passages each of which has a flat sectional shape andthrough which exhaust gas generated by a combustion flows, wherein theplurality of exhaust gas passages are laminated so as to be disposed insubstantially parallel with each other; a tank containing the pluralityof exhaust gas passages; a water passage formed in the tank throughwhich cooling water flows to exchange heat with the exhaust gas passingthrough the plurality of exhaust gas passages; a cooling water inletpipe disposed on the tank through which the cooling water flows into thetank; a cooling water outlet pipe disposed on the tank through which thecooling water is exhausted from the tank; and a water flow regulatingmeans provided in the water passage close to an upstream side of theplurality of exhaust gas passages for regulating a stream of the coolingwater at a vicinity of the upstream side of the plurality of exhaust gaspassages.
 16. An exhaust gas heat exchanger according to claim 15,wherein the water flow regulating means is provided close to a innerwall of the tank with respect to the cooling water inlet pipe, which isopposite to the cooling water inlet pipe and where the cooling watercoming into the tank through the cooling water inlet pipe collides. 17.An exhaust gas heat exchanger according to claim 15, wherein the waterflow regulating means has a wall-like shape serving as a wall regulatinga direction of stream of the cooling water.
 18. An exhaust gas heatexchanger comprising: a plurality of exhaust gas tubes through whichexhaust gas generated by combustion flows; a casing in which theplurality of exhaust gas tubes are arranged, defining a fluid passagetherein through which fluid flows around the plurality of exhaust gastubes to exchange heat with the exhaust gas; a fluid inlet disposed onthe casing at an inlet side of the plurality of exhaust gas tubesthrough which the fluid flows into the casing along a directionsubstantially perpendicular to a longitudinal direction of the pluralityof exhaust gas tubes; and an outer space defined between an inner wallof the casing and an outermost exhaust gas tube of the plurality ofexhaust gas tubes, and extending longitudinally in a directionsubstantially parallel with an inflow direction of the fluid flowinginto the casing through the fluid inlet, wherein: a width of the outerspace, in a direction substantially perpendicular to the inflowdirection of the fluid and substantially perpendicular to thelongitudinal direction of the plurality of exhaust gas tubes, issubstantially equal to that of an inner space defined between adjacentexhaust gas tubes.
 19. An exhaust gas heat exchanger comprising: aplurality of exhaust gas tubes through which exhaust gas generated bycombustion flows; a casing in which the plurality of exhaust gas tubesare arranged, defining a fluid passage therein through which fluid flowsaround the plurality of exhaust gas tubes to exchange heat with theexhaust gas; a fluid inlet disposed on the casing at an inlet side ofthe plurality of exhaust gas tubes, through which the fluid flows intothe casing along a direction substantially perpendicular to alongitudinal direction of the plurality of exhaust gas tubes; and anouter space defined between an inner wall of the casing and an outermostexhaust gas tube of the plurality of exhaust gas tubes, and extendinglongitudinally in a direction substantially parallel with an inflowdirection of the fluid flowing into the casing through the fluid inlet,wherein: a width of the outer space, in a direction substantiallyperpendicular to the inflow direction of the fluid and substantiallyperpendicular to the longitudinal direction of the plurality of exhaustgas tubes, is equal to or greater than 1 mm but equal to or less than 5mm.
 20. An exhaust gas heat exchanger according to claim 18, whereineach exhaust gas tube has a flat sectional shape, and the plurality ofexhaust gas tubes are laminated in a thickness direction thereof withthe inner space defined between adjacent exhaust gas tubes, and whereinthe inflow direction of the fluid is substantially perpendicular to alaminated direction of the plurality of exhaust gas tubes.
 21. Anexhaust gas heat exchanger according to claim 18, further comprising: afluid outlet disposed on the casing through which the fluid flows outfrom the casing in a direction substantially perpendicular to thelongitudinal direction of the plurality of exhaust gas tubes; and anoutlet side outer space defined between the inner wall of the casing andthe outermost exhaust gas tube at the vicinity of the fluid outlet,extending longitudinally in a direction substantially perpendicular toan outflow direction of the fluid flowing out from the casing, wherein:a width of the outlet side outer space, in a direction substantiallyparallel with the outflow direction of the fluid, is greater than thatof the inner space defined between adjacent exhaust gas tubes.
 22. Anexhaust gas heat exchanger according to claim 18, further comprising: afluid outlet disposed on the casing, through which the fluid flows outfrom the casing in a direction substantially perpendicular to thelongitudinal direction of the plurality of exhaust gas tubes; and anoutlet side outer space defined between the inner wall of the casing andthe outermost exhaust gas tube at the vicinity of the fluid outlet,extending longitudinally in a direction substantially perpendicular toan outflow direction of the fluid flowing out from the casing throughwhich the fluid outlet, wherein: a width of the outlet side outer space,in a direction substantially parallel with the outflow direction of thefluid, is equal to or greater than 5 mm.
 23. An exhaust gas heatexchanger according to claim 18, further comprising: a side spacedefined between a side inner wall of the casing and the plurality ofexhaust gas tubes, extending longitudinally in a direction substantiallyperpendicular to the inflow direction of the fluid, wherein a width ofthe side space, in a direction substantially parallel with the inflowdirection of the fluid, is equal to or greater than that of the innerspace defined between adjacent exhaust gas tubes.
 24. An exhaust gasheat exchanger according to claim 18, further comprising: a side spacedefined between a side inner wall of the casing and the plurality ofexhaust gas tubes, extending longitudinally in a direction substantiallyperpendicular to the inflow direction of the fluid, wherein a width ofthe side space, in a direction substantially parallel with the inflowdirection of the fluid, is equal to or greater than 1 mm.
 25. An exhaustgas heat exchanger according to claim 18, further comprising: a fluidflow regulating means provided in the fluid passage close to an upstreamside of the plurality of exhaust gas tubes for regulating a stream ofthe fluid at a vicinity of the upstream side of the plurality of exhaustgas tubes so that the fluid after colliding with a side inner wall ofthe casing is led toward an upstream side of the plurality of exhaustgas tubes.
 26. An exhaust gas heat exchanger according to claim 19,wherein each exhaust gas tube has a flat sectional shape, and theplurality of exhaust gas tubes are laminated in a thickness directionthereof with an inner space defined between adjacent exhaust gas tubes,and wherein the inflow direction of the fluid is substantiallyperpendicular to a laminated direction of the plurality of exhaust gastubes.
 27. An exhaust gas heat exchanger according to claim 19, furthercomprising: a fluid outlet disposed on the casing through which thefluid flows out from the casing in a direction substantiallyperpendicular to the longitudinal direction of the plurality of exhaustgas tubes; and an outlet side outer space defined between the inner wallof the casing and the outermost exhaust gas tube at the vicinity of thefluid outlet, extending longitudinally in a direction substantiallyperpendicular to an outflow direction of the fluid flowing out from thecasing, wherein: a width of the outlet side outer space, in a directionsubstantially parallel with the outflow direction of the fluid, isgreater than that of the inner space defined between adjacent exhaustgas tubes.
 28. An exhaust gas heat exchanger according to claim 19,further comprising: a fluid outlet disposed on the casing, through whichthe fluid flows out from the casing in a direction substantiallyperpendicular to the longitudinal direction of the plurality of exhaustgas tubes; and an outlet side outer space defined between the inner wallof the casing and the outermost exhaust gas tube at the vicinity of thefluid outlet, extending longitudinally in a direction substantiallyperpendicular to an outflow direction of the fluid flowing out from thecasing through which the fluid outlet, wherein: a width of the outletside outer space, in a direction substantially parallel with the outflowdirection of the fluid, is equal to or greater than 5 mm.
 29. An exhaustgas heat exchanger according to claim 19, further comprising: a sidespace defined between a side inner wall of the casing and the pluralityof exhaust gas tubes, extending longitudinally in a directionsubstantially perpendicular to the inflow direction of the fluid,wherein a width of the side space, in a direction substantially parallelwith the inflow direction of the fluid, is equal to or greater than thatof the inner space defined between adjacent exhaust gas tubes.
 30. Anexhaust gas heat exchanger according to claim 19, further comprising: aside space defined between a side inner wall of the casing and theplurality of exhaust gas tubes, extending longitudinally in a directionsubstantially perpendicular to the inflow direction of the fluid,wherein a width of the side space, in a direction substantially parallelwith the inflow direction of the fluid, is equal to or greater than 1mm.
 31. An exhaust gas heat exchanger according to claim 19, furthercomprising: a fluid flow regulating means provided in the fluid passageclose to an upstream side of the plurality of exhaust gas tubes forregulating a stream of the fluid at a vicinity of the upstream side ofthe plurality of exhaust gas tubes so that the fluid after collidingwith a side inner wall of the casing is led toward an upstream side ofthe plurality of exhaust gas tubes.